Processing Element consume frequency

[pilipovicn]

Added the parameters that specify how often do PEs consume flits, and how many of them, as well as internal PE input buffer depth. Default for all this is 1, which makes no difference. For those who need this functionality, eg. they can slow down the PE consume frequency to better model a system.

[davidepatti]

thank you for the contribution, I will test and eventually merge it if there are no problems.